The present invention relates to acoustical devices and particularly to a highly directional sound source for an acoustical inspection device. Acoustical devices utilizing sound sources for generating acoustical waves that impinge upon a surface are used to inspect various materials. In addition, such devices have been used to map the formation surrounding a borehole, as for example as shown in U.S. Pat. No. 2,825,044. In this patent a sound source is used to generate a highly directional acoustical pulse which travels radially and penetrates into the formation surrounding the borehole. Means are provided for detecting the reflected acoustic wave and recording a characteristic of the reflected acoustic wave.
Similar devices to that described in the patent have also been used to provide a map of the prominent characteristics of the well bore formations, for example the locations of fractures in the rock formations surrounding a borehole. In this type of mapping device the amplitude of the reflected signal is recorded in relation to the position of the tool in the borehole. All of the above devices require the use of a highly directional sound source for producing acoustic waves. To obtain directionality one must use either an extremely large sound source or extremely high frequencies. The use of large sound source causes problems in the physical size of the device and limits its usefulness. The use of high frequencies reduces the penetration of the acoustic energy and, thus, limits the usefulness of the device.